Rms voltage regulator



I S/ARASE RMS VOLTAGE REGULATOR Sept. 30, 1969 Filed July 5. 1967 I INVENTOR Arrow/(5W5 United States Patent.

3,470,451 RMS VOLTAGE REGULATOR Shingo Arase, Monterey Park, Calif., asslgnor to Hoffman Electronics Corporation, El Monte, Califl, a corporation of California Filed July 3, 1967, Ser. No. 650,720 Int. Cl. H02m 1/08, 7/04 US. Cl. 321-18 8 Claims ABSTRACT OF THE DISCLOSURE A voltage regulator for maintaining the RMS value constant in which the negative going half of the input signal is used to change the reference level of a Zener diode which in turn controls the base level of a series transistor to cause it to clip at a lower level if the input voltage increases.

Background of the invention Many difierent techniques have been advanced for providing a regulated voltage Whose RMS value or heating energy is constant regardless of variations in input voltage. Such a requirement is present, for example, in circuits where it is necessary to keep constant the temperature of vacuum tube filaments. Most such systems require relatively complicated feedback circuits and line filtering to obtain a relatively rippleless DC voltage at the output. Such systems are expensive and the filtering capacitors required are heavy and bulky and thus undesirable for many applications.

Summary of the invention The present invention takes advantage of the fact that a constant load such as a tube filament is not affected by the shape of the waveform it receives, only by its energy content. This constant energy content, or RMS value of a rectified voltage can be maintained constant by keeping the area of the voltage half-cycles equal by reducing the peak value of any half cycle, the magnitude of which tends to increase because of an increase in input voltage.

Brief description of the drawing FIGURE 1 is a schematic diagram of the circuit of the present invention; and FIGURE 2 illustrates the output thereof.

Description of the invention In the present invention, as illustrated by FIGURE 1, the input alternating current voltage is applied to input terminals 10 and 12 to which is connected the primary 14 of transformer 16. The secondary winding 18 of the transformer 16 is center-tapped and has its ends connected to diodes 20 and 22 respectively to form a full wave rectifier. The junction point of the diodes 20 and 22 is connected through a resistor 2-4 to the emitter of a PNP power transistor 26, the collector of which is connected to an output terminal 28, the other output terminal 30 being grounded.

The base of the transistor 26 is connected to the collector of the NPN driver transistor 32 whose emitter is also connected to the output terminal 28. The base of the transistor 32 is connected to the junction 35 of the resistor 34 and diode 36. The other end of the resistor 34 is connected to a source of positive potential while the 3,470,451 Patented Sept. 30, 1969 cathode of the diode 36 is connected to a Zener diode 38. The Zener diode 38 is connected to ground through a resistor 40.

The junction 39 of the Zener diode 38 and the resistor 40 is connected to another resistor 42 whose other end is connected through a pair of diodes 44 and 46 to the upper and lower ends respectively, of the secondary winding 18. The junction of the resistor 42 and the diodes 44 and 46 is also connected to ground through a capacitor 48.

The regulating circuit of the present invention operates as follows: Let it be assumed that the upper end of the secondary 18 is positive going. As a result, a current flows through the upper half of the Winding 18, the diode 20, resistor 24 and transistor 26 to the output and then back to the center tap of the transformer. The conduction of the transistor 26 is controlled by the transistor 32 which in turn is controlled by the voltage appearing at the junction 35 between the resistor 34 and the diode 36. Because of the presence of the Zener diode 38, the voltage at the junction point 35 is at a given potential above the voltage at the junction point 39, depending on the rating of Zener diode 38. The potential at the emitter of the transistor 32 follows its base and is thus established by the potential at junction 35. When the input voltage reaches the base voltage of the transistor 32, that is, the base voltage of transistor 26, the transistor 26 starts to clip. This action is shown by the curve '50 in FIGURE 2. The dotted portion of this curve represents the input voltage.

The voltage at the junction point 39 is dependent upon the magnitude of the input voltage. Still assuming that the upper end of the secondary 18 of transformer 16 is positive, it can be seen that a current flows from the center-tap of the "secondary 18 through the resistor 40, the resistor 42, and the diode 46 back to the lower end of the secondary winding 18 and the center-tap thereof is inverse or negative with respect to the voltage between the center-tap and the upper end of the secondary and, therefore, the voltage drop across the voltage divider made up of the resistors 40 and 42 will be a negative voltage, that is, it will be below ground potential. The voltage at the junction point 39 will be dependent upon the values of the resistors 40 and 42 and upon the magnitude of the input voltage.

As the input voltage increases, the voltage at the junction point 39 will become more negative, that is, further below ground. Since the voltage at the point 35 is a fixed amount above that at the point 39, a decrease in the voltage at the point 39 will cause a corresponding decrease at point 35. This will reduce the base voltage of the transistor 32 and cause the transistor 26 to clip the voltage at a lower level. This is shown by curve 52 of FIG- URE 2 where again, the dotted portion represents the input voltage. The areas under the solid lines of curves 50 and 52 are equal as a result of the lower clipping level. Consequently, a voltage having a constant RMS value is supplied to the load.

In the circuit illustrated, the resistor 24 is a current limiting resistor which is useful to protect the transistor 26 when the load is of low value, for example, when the filament of a vacuum tube is cold. The diode 36 is provided for temperature compensation to compensate for the variations with temperature of the base-to-emitter drop of the transistor 32. The capacitor 48 is not required, but is useful to maintain the voltage at the junction point 39 constant between half cycles. The power transistor 26 is also not required for some applications but provides more power to a lower impedance.

As can be seen from the foregoing description, a regulator circuit has been provided that will maintain the RMS value of an output voltage supplied to a load constant regardless of changes of the input voltage. This is accomplished without the necessity of line filtering or complicated feedback circuits.

The invention may be embodied in other specifi forms not departing from the spirit or central characteristic thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive.

I claim:

1. A regulator circuit comprising rectifier means; means for applying an input voltage to said rectifier means; regulating means having an input electrode, an output electrode and a control electrode; means coupling the input electrode of said regllating means to said rectifier means; an output terminal means coupling said output terminal to said output electrode of said regulating means; means for establishing a point of control potential; means coupling said point of control potential to said control electrode of said regulating means; means for establishing a voltage inverse to that produced by said rectifier means; and means coupled to said inverse voltage establishing means and said point of control potential for varying the potential of said point in response to variations in said input voltage.

2. The circuit of claim 1 wherein said means coupling said inverse voltage establishing means and said point of control potential comprises a Zener diode and means for varying the baseline reference of said Zener diode.

3. The circuit of claim 2 wherein said means for varying the baseline reference comprises a voltage divider coupled across said means for establishing an inverse voltage.

4. A regulator circuit comprising a transformer having a primary winding and a center-tapped secondary winding; means for applying an input voltage to said primary winding; first and second diodes connected to the upper and lower ends of said secondary winding respectively, said diodes being poled in the same direction and having their ends remote from said secondary winding connected together; regulating means having an input electrode, an output electrode and a control electrode; means connecting said input electrode of said regulating means to the junction of said ends of said diodes; a pair of output terminals; means for connecting a first of said output terminals to the output electrode of said regulating means; means connecting the other of said output terminals to said center-tap of said secondary winding; a source of -direct current potential; a series circuit'comprising a first resistive means, a Zener diode and a second resistive means connected between said source of direct current potential and said center-tap of said secondary winding; means connecting the junction between said first resistive means and said Zener diode to said control electrode of said regulating means; third resistive means; third and fourth diodes connecting one end of said third resistive means to the upper and lower ends. respectively of said secondary winding; said third and fourth diodes being poled in a direction opposite to said first and second diodes; and means connecting the other end of said third resistive means to the junction of said Zener diode and said second resistive means.

5. The circuit of claim 4 wherein said one end of said third resistive means is connected to said center-tap of said secondary winding by a capacitor.

6. The circuit of claim 4 wherein said center-tap of said secondary winding is grounded.

7. The circuit of claim 4 wherein a diode is connected between said first resistive means and said Zener diode.

8. The circuit of claim 4 wherein said regulating means comprises a transistor and wherein said means connecting said junction of said first resistive means and said Zener diode to said control electrode of said regulating means comprises a second transistor.

References Cited UNITED STATES PATENTS 3,287,619 11/1966 Burson 32116 3,310,727 3/1967 Flannery 32118 X 3,386,030 5/1968 Kann 323-4 OTHER REFERENCES Battery Charger, IBM Technical Disclosure Bulletin, vol 7, No. 6, November 1964, p. 432.

LEE T. HIX, Primary Examiner A. D. PELLINEN, Assistant Examiner US. Cl. X.R. 307-297; 323-22, 39 

